1. Technical Field
The present invention relates to a light emitting diode circuitry, especially to a light emitting diode circuitry applied to light emitting diode displays.
2. Description of the Prior Art
Liquid crystal displays (LCDs) and light emitting diode (LED) displays are widely used nowadays. Because liquid crystal displays and LED displays have slim shapes, low power dissipation and low radiation, liquid crystal displays and LED displays gradually replace traditional CRT (cathode ray tube) monitors and are widely used in mobile electronic devices such as notebooks and PDAs (personal digital assistants).
Compared to LCDs, organic light emitting diode (OLED) displays are capable of self-emitting light and have wider viewing angle, higher contrast, lower operating voltage, faster dynamic response, brighter color, simpler manufacturing process and thinner thickness, thus they are gradually replacing LCDs. In OLED display manufacturing procedures, a bias voltage is applied to an OLED, to make the inner electrons and electric holes pass through the hole transport layer and the electron transport layer, then add an organic material having light emitting characteristic into the OLED. The organic material will combine with the OLED to form an exciton to release energy. After energy is released, the exciton returns to the ground state. The energy can be released in various colored light, and the color is determined by the characteristic of chosen materials. However, comparing with liquid crystal displays and LED displays, the service life of OLED displays are still relatively short.
Please refer to FIG. 1, FIG. 1 shows a related art LED circuitry 100. As shown in FIG. 1, the LED circuitry 100 includes a first transistor M1, a second transistor M2, a storage capacitor Cst and an LED D1. The first end of the first transistor M1 is electrically coupled to a data line DATA, and the control end of the first transistor M1 is electrically coupled to a scan line SCAN. The first end of the second transistor M2 is electrically coupled to a first power source VDD, and the control end of the second transistor M2 is electrically coupled to a second end of the first transistor M1. The first end of the capacitor Cst is electrically coupled to the first power source VDD, and the second end of the capacitor Cst is electrically coupled to the second end of the first transistor M1. The anode of the light emitting diode D1 is electrically coupled to the second end of the second transistor M2, and the cathode of the light emitting diode D1 is electrically coupled to a second power source VSS. The voltage level of the first power source VDD is high, and the voltage level of the second power source VSS is low. When the first transistor M1 is turned on by the scan line SCAN, the first transistor M1 will receive signals from the data line DATA and store voltage into the storage capacitor Cst, after that, the first transistor M1 controls the second transistor M2 according to the received signals to make the light emitting diode D1 emit light. However, under this configuration, the voltage level of the cathode of the light emitting diode D1 will gradually become higher, causing the current following from the first power source VDD through the light emitting diode D1 become smaller, thus deteriorating the image retention effect of displays. Further, if replacing the light emitting diode D1 with an OLED, the total service life of the light emitting diode circuit 100 will be greatly reduced.